I am developping a website intended to mobile phones and I've got a contact section with a mailto: tel: for the mail and telephone, is there any similar function that would make a call to the default gps app of the phone and preload it with GPS coordinates ?
For android:
<a href="geo:37.786971,-122.399677;u=35">open map</a>
For iphone:
<a href="http://maps.apple.com/?q=cupertino">Cupertino</a>
If you want to use coordinates instead of location name, see here for details
(Found them on net, not tested.)